FRUITS AND FRUIT PRODUCTS Symposium presented before the Division of Agricultural and Food Chemistry a t the 100th Meeting of the American Chemical Society, Detroit, iMich.
Processing of Apple Juice ROY E. MARSHALL Michigan Agricultural Experiment Station, East Lansing, Mich.
MERICA has become juice conscious during the past decade. Ten years ago not more than 2 million cases of fruit and vegetable juices were processed commercially, and more than half of that amount was tomato juice, which was then in its third season of commercial production. Probably 35 million cases of fruit and vegetable juices were processed during 1939. This is a phenomenal growth, and leads one to say that Americans are drinking a substantial portion of the fruits and vegetables they used to eat. The processing of apple juice, often improperly designated as cider, had been attempted by numerous individuals in various parts of the country for many decades, but every commercial venture prior to 1935 ended in failure. Consumer interest could not be developed sufficiently to justify commercial production. Lack of interest in the product was due to failure on the part of processors to avoid the development of off-flavors, particularly pasteurized or cooked flavors caused by caramelization. The usual method of sterilization of fruit and vegetable juices was holding pasteurization. This method had been used successfully with grape juice for many years. Essentially it consisted in filling containers with juice, sealing them, and then placing the filled containers in a steam or hot water bath where the temperature of the juice was raised to and held a t 170" F. for 20 t o 30 minutes. Most fruit can be subjected to such treatment without ill effect, but apple juice is so delicately flavored that it invariably develops an undesirable pasteurized taste which masks the true apple flavor. During the first half of the past decade, several investigators thought that germ-proofing filtration, sometimes called "cold sterilization", might solve this important phase of the apple juice problem. Carpenter and associates ( I ) concluded that fruit juices could be sterilized by filtration through the Seitz germ-proofing filter, but they cautioned the strict observation of certain operating conditions. The writer and associates (3, 6) found that the juice leaving a properly operated germ-proofing filter is sterile, but that there is danger of introducing microorganisms into the juice after it is sterilized and before the container is sealed. (A tabulation of results covering several seasons showed that juice in about 3 per cent of the containers developed mold mycelium.) They also found that apple juice subjected t o certain clarifying treatments before germ-proofing filtration often deposited an unattractive, amorphous sediment after 2-4 weeks storage at room temperatures. Two or three commercial plants are using this method of sterilization for apple juice
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a t present, but it is not so popular in this country as in Europe.
Flash Sterilization I n 1933 Mottern and von Loesecke (9) described an experimental flattened tube, coiled in a steam jacket, which was found very satisfactory for citrus juices. The senior author suggested to the writer that this type of flash sterilizer might also be suitable for processing apple juice. A small unit was constructed and operated during February, March, and April, 1937. The apple juice thus processed was unanimously pronounced the best in both appearance and taste of any produced by several methods during that season (7). Another coiled flattened-tube sterilizer suitable for operation in plants of small capacity was constructed during the fall of 1938, and a supplementary report issued in 1939 (8). The tubes for conducting the juice through the steam jacket are usually made of Monel metal. Tubes of 0.5-inch diameter are used for plants of small capacity, but where capacities of 200 to 400 gallons per hour are desired, 1-inch Monel tubing is used. Some 25 lineal feet of this 1-inch tubing is flattened to give an inside thickness of 0.25 inch. Flattening of tubes reduces the ratio of cross-sectional area to tube inner surface or periphery, and thus increases the rate of heat transfer from steam to juice. It makes for increased velocity and agitation of the juice, and results in uniform heating. This, together with the fact that the juice is heated in a closed system, makes it possible to raise the temperature of the juice to the pasteurizing point without caramelization and the objectionable cooked or pasteurized taste. The flattened and coiled tube is usually enclosed in an 8-inch iron casing. Steam, a t a pressure of perhaps 25 pounds per square inch, is delivered into the chamber in which the flattened coiled tube is located. The maximum temperature to which the juice is heated is governed by a thermostat regulating steam volume. Under these conditions it is usually possible to raise the temperature of the juice from 50" or 60" F. to the proper pasteurizing point in 2 to 5 seconds. In our early work the temperature of the juice was raised to 190" F. Subsequently we found that 160" F. is ample and that the quality of the product is much superior when operating a t the lower levels. For commercial practice we recommend 170" F. This hot juice is delivered directly into nonsterile bottles 285
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INDUSTRIAL AND ENGINEERING CHEMISTRY
or enamel-lined cans. Investigations a t several stations show that apple juice fades in color and rapidly deteriorates in quality when plain tin containers are used. The cans are filled from the bottom to avoid foaming and t o prevent aeration. Furthermore, the containers are completely filled (no head space) to exclude air as recommended by Pederson and Tressler (IO). They are then inverted, or caused to roll on their sides, to bring the hot juice in contact with the cover or crown. On cooling, these containers should develop 13 to 18 inches of vacuum. Pederson and Tressler (IO) showed that juice processed in this manner is not sterile. The yeasts are killed, the mold organisms are held in check by the absence of air, and the surviving bacteria cannot grow in apple juice.
Quick Cooling The next important step in processing is cooling the container with its juice to less than 120" F. The cooling should start soon after closing. We usually start the cooling process about 30 seconds after closing. Ijnless the juice is cooled promptly, the prolonged period of high temperatures results in deterioration of quality and often some sedimentation. Cooling is accomplished by causing the filled containers to revolve in a horizontal position under a spray of cold water for 1 to 2 minutes, During the past year Kremer and the writer found that the optimum rate of rotation for the filled container is approximately 100 r. p. m. Very rapid rotation causes the juice to revolve with the container and develop an air space a t the center of the liquid rather than a t the top.
Cloudy and Clear Juice The preceding paragraphs deal with processing or heat treating methods. There are other problems in handling the juice prior to processing that deserve brief comment. Some investigators and packers prefer t o merchandise only clarified and filtered juice, others think that the consuming public will be as interested in a cloudy apple juice as it is in cloudy grapefruit or pineapple juice. The writer favors the
SOME OF THE EQUIPMENT USED I N MAKING
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former because several consumer-demand studies conducted in Michigan (6) showed that the consumer prefers the clear juice to such an extent that he is willing t o pay a premium for it. It is reasonable to assume, however, that consumers in some areas may have a preference for cloudy juice, and under such circumstances it would be foolish to clarify and filter. Fresh apple juice filters slowly and with difficulty. Some clarifying treatment that will break down or aggregate the suspended colloidal material is recommended if the juice is to be filtered. The gelatin-tannin method, as modified by Carpenter and Walsh ( 2 ) , is still used by a few packers, but most of them insist on simple and convenient treatments that will result in more rapid filtration. Likewise, the coagulation of the suspended material by flash heating (9) has not been popular with apple juice producers. The most satisfactory method of clarification is by an enzyme which disintegrates a portion of the pectin and causes precipitation of the materials that cause cloudiness in the juice. The enzymic method was developed for apple juice by Kertesz (4) and has subsequently been merchandised as Pectinol. Sipple (1I ) recently developed a method in which bentonite is used t o flocculate the suspended material in apple juice. He reports good results, but the writer has been unable to obtain a satisfactory rate of filtration with juice so treated. There is great need of a clarification method for apple juice that is as simple and as effective as the enzymic method but much less expensive.
Deaeration Sipple (11) favors deaeration of apple juice prior to processing, claiming that deaerated juices retain the apple flavors and physical appearances better than nondeaerated juices. Pederson and Tressler (IO)recommend deaeration for cloudy juice but regard it as unessential for clarified and filtered juice. Seven pairs of deaerated and nondeaerated lots of dear apple juice were processed during the past year a t the Michigan Experiment Station, and examinations made after warehousing for 6 months failed t o show any appreciable differences between the treatments. In fairness t o deaeration, it
EXPERIMENTAL PACKS OF APPLE JUICE AT THE
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EXPERIMENT STATION
A is ftash sterilizer with juice intake a t 1; steam intake is through 2 t o casing 3 which encloses t h e flattened and coiled tubing. Bottles may be filled by the siphon fillers, 4, which are connected by rubber tubing to the ooil of flattened tubing, Cans are filled with rubber tube 5. B is a n automatic closing machine. When t h e closed cans leave this machine, they invert onto the belt of C, which delivers them t o the cooler a t D . This can cooler consists of a belt moving 100 feet per minute, which causes the 20-ounce cans t o rotate approximately 100 r. p. m. while being moved forward slowly under a spray of cold water.
March, 1941
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
should be stated that while the pressure in the deaerating chamber was only 0.7 inch of mercury, the juice was subsequently exposed to room conditions that permitted some surface aeration. The juice in the sealed containers showed 72 to 80 per cent total gas removal. Furthermore, the containers were type L tin-plate cans lined with a special juice enamel coating. On the basis of these tests we do not feel that deaeration is so essential in the handling and processing of apple juice. Modern apple juice processing is entering its third or fourth season. All processors operating in 1939 in Michigan will process on much larger scales in 1940, and several new plants are now being installed. It is possible that the value of the pack in Michigan may reach a million dollars during the coming year. Packers and prospective packers in other states may equal or surpass the Michigan pack.
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Literature Cited Carpenter, D. C., Pederson, C. S., and Walsh, W. F., IND. ENG. CHEM.,24, 1218-23 (1932). Carpenter, D. C., and Walsh, W. F., N. Y. State Agr. Expt. Sta., Tech. BUZZ.202 (1932). Fabian, F. W., and Marshall, R. E., Mich. Agr. Expt. Sts., Circ. Bull. 98 (1935). Xertesz, 2. I., N. Y. State Agr. Expt. Sta., Bull. 589 (1930). Marshall, R. E., Fruit Products J., 16, No.11, 328-9,331 (1937). Marshall, R. E., Mich. Agr. Expt. Sta. Quart. Bull., 14, No. 3, 208-14 (1932). Marshall, R. E., and Kremer, J. C., Ibid., 20, No. 1, 28-34 (1937). Ibid., 21, No. 1, 12-17 (1938). Mottern, H. H., and Loesecke, H. W. von, Fruit Products J . , 12, NO.6, 325-6 (1933). Pederson, C. S., and Tressler, D. K., IND. ENQ.CHBM.,30, 954-9 (1938). Sipple, H.L.,et al., Fruit Products J . , 19, No. 6, 167-87 (1940).
Citrus Pectates
PROPERTIES, MANUFACTURE, AND USES
W. E. BAIER AND C. W. WILSON California Fruit Growers Exchange, Ontario, Calif.
Pectates result from the saponifkation of pectins. Treatment of commercial pectin with an alkali will form a type of pectate that has been known since 1790. Treatment of protopectin under proper conditions gives a different type of pectate, characterized by more viscosity in aqueous sols, and an alcohol precipitate which is stringy and fibrous rather than amorphous as is the case for ordinary types of pectate. The viscous type may be irreversibly transformed into the less viscous or ordinary type by acid treatment. Chemical relation of the two types is discussed. Both types of pectates form gelatinous salts with alkaline earth or heavy metals. Sodium pectate is a typical hydrophilic colloid, which forms gels a t low concentrations and hence very cheaply. Sols tend to remain on the surface of paper, and
ECTIC substances are widely distributed in plants, being present a t some stage in the growth of practically all vegetable materials. Pectin (the jelly-making substance in fruits) is the only pectic substance so far commercialized. Another, pectic acid, has been widely investigated both chemically and as regards its functions in the plant. Exploration of possible industrial applications of this and related pectic substances is a practically untouched field, Upon treatment with cold dilute alkali (sodium hydroxide), pectin hydrolyzes and depolymerizes to yield moderately viscous, soluble pectates or salts of pectic acid. The corresponding alkaline earth salts are insoluble. The soluble pectates form alcohol precipitates which are granular gels. To obtain pectates, the sols of which are very viscous and which yield precipitates with alcohol that are in the form of visible fibers, it is necessary to start from the plant material in an earlier stage, protopectin. If this protopectin is treated with alkali, 8, pectate results whose alkaline earth salts are likewise insoluble but whose alkali salt solutions are highly viscous and form fibrous precipitates with alcohol.
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hence pectates are poor adhesives but may be used to prevent substances from sticking to paper, etc. This property may also be used in coating building board to retard penetration of paint. If continuous, pectate films are generally impervious to oils and this property has suggested their use in treatment of paper, the air permeability also being reduced. A crude material is suggested for this work and for such other uses as thickening or concentrating rubber latex or for modifying the rate a t which water quenches heated steel. A wide range of severity of quench may be obtained by varying the concentration. Certain heavy metal pectates are water repellent, and this property suggests a preparation of nonhygroscopic fillers for plastics. Other uses are discussed.
Both types of pectates will withstand boiling in neutral or mildly alkaline solutions without appreciable change, whereas if pectin is boiled with alkali, it is converted largely to nonviscous materials no longer capable of yielding calcium precipitates (6). When acidified, pectates give pectic acid from which only the nonfibrous pectate may be regenerated upon neutralization. Figure 1 shows this relation. Acid P r o t o p e c t i n w P e o t i n
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Cold Alkali
Fibrous Peotat-Pectic
Hot Alkali
Cold Alkali
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Nonfibrous Peotate Acid
Acidi
Low-Viscosity Degradation Products (Calcium Salts Soluble)
p a l i Acid
FIGURE 1. RELATION OB'PECTIC SUBSTANCES
